For assembling of semiconductor devices, bonding apparatuses are used such as die bonding apparatuses for mounting a semiconductor die on a substrate or a lead frame and wire bonding apparatuses for wire-connecting electrodes on a semiconductor die mounted on a substrate and electrodes on the substrate. In wire bonding apparatuses, a substrate sucked and fixed to a bonding stage or a semiconductor die mounted on the substrate is heated up to about 200 to 250 degrees C. and a bonding tool such as a capillary is used for thermal compression of a thin wire of, for example, gold, silver, or copper with an ultrasonic vibration applied thereto to electrodes on the substrate or the semiconductor die so that the metal thin wire is bonded to each electrode. Also, die bonding apparatuses employ a system in which a substrate sucked and fixed to a bonding stage with adhesive applied thereto is heated, onto which a semiconductor die is thermally compressed and then the adhesive is thermally cured so that the semiconductor die is fixed to the substrate or a system in which a lead frame sucked and fixed to a bonding stage is heated up to about 300 to 450 degrees C., onto which a semiconductor die is eutectically bonded so that the semiconductor die is fixed to the lead frame. Nowadays, flip-chip bonding methods are also employed in which bumps (projections) of, for example, solder are formed on electrodes on a substrate and electrodes on a semiconductor die in advance, and the semiconductor die is reversed and, with being held by a collet such that the electrodes are opposed to the substrate (face downward), heated so that the bumps become melted, while the substrate, which is sucked and fixed to a bonding stage, is heated up to about 200 degrees C. so that the bumps become melted, and then the bumps are brought into contact with each other to form a metallic bond so that the semiconductor die is bonded to the substrate. In such bonding apparatuses, it may be necessary for the substrate sucked and fixed to the bonding stage to be heated up to a temperature of about 200 degrees C. during bonding.
When the bonding stage is heated up to about 200 degrees C., the air over the bonding stage is heated by the bonding stage to move upward. The surrounding cold air then comes over the bonding stage and is heated by the bonding stage to move upward again, causing a circulation of air. Upon this, airs of different temperatures, that is, different densities due to rising air are mixed to cause air turbulence over the bonding stage.
Meanwhile, in such bonding apparatuses, the surface of the substrate sucked and fixed to the bonding stage or the semiconductor die mounted on the substrate are imaged and, based on the images, the positions of the electrodes on the substrate and the semiconductor die or the bonding position of the substrate are detected and, based on the detected positions, the position of the bonding tool is controlled. Air turbulence, if occurred over the bonding stage as described above, would come into the field of view of the imager for imaging the substrate sucked and fixed to the bonding stage or the semiconductor die, suffering from a problem that the accuracy of detection of the imaging position may decrease. To address this, there has been proposed a method of blowing nitrogen gas or air into the field of view of the imager to blow off the air turbulence for improvement in the accuracy of position detection by the imager (see Patent document 1, for example).